What grain is fermented to produce ethanol, commonly used as a fuel?

The correct answer is corn, as it is the primary grain used in the fermentation process to produce ethanol, particularly in the United States. Corn is favored for ethanol production due to its high starch content, which can be easily converted into sugars during fermentation. This process involves breaking down the starches into simple sugars, which yeast can then ferment into ethanol and carbon dioxide.

In the U.S., the majority of ethanol is produced from corn because it is widely grown and readily available. Its extensive agricultural infrastructure supports large-scale production, making it economically viable. Other grains like wheat, barley, and rice can also be fermented to produce ethanol, but they are less commonly used for this purpose compared to corn, which has the highest yield and efficiency in conversion to ethanol.